Static Transfer Switches (STS) are designed to transfer supply between independent one-phase or three-phase AC power sources. Unlike traditional automatic transfer switches (ATS), STS provides 20 times faster load transfer (typically 1/4 of a cycle), which ensures the uninterrupted operation of even the most sensitive electronic equipment. Load retransfer to a preferred input source is virtually instantaneous (typically 100 µs). The basic applications of STS are in automatic systems for power industry, power supply systems for petrochemical industry, computer and telecommunication centres, operating theatres, intensive care units, automatic and security systems of 'intelligent' buildings as well as other equipment which is highly sensitive on supply interruption. It's high overload capacity and transfer algorithm enables rapid fuse blow during short-circuits. In consequence voltage immediately returns to normal value to supply other loads. The built-in transient voltage surge suppression system for SCR switches provides additional protection against damage to supplied devices.